FLUIDIZED-BED REACTOR FOR THE TREATMENT OF FLUIDIZABLE SUBSTANCES AND PROCESS HEREFOR

Abstract

This invention relates to a fluidized-bed reactor (1) for the chemical and/or physical treatment of fluidizable substances and to a process herefor. Into the reactor interior (2), process gas is introduced via at least one central tube (3) and fluidizing gas via a tuyere bottom (7). The metallic walls of the central tube (3), of a container (4) connected with the same, and of an annular space (9) provided below the tuyere bottom (7) are provided with a thermal insulating coating (6, 10).

This invention relates to a fluidized-bed reactor for the chemical and/or physical treatment of fluidizable substances in a reactor interior, comprising at least one central tube for introducing process gas into the reactor interior and a tuyere bottom for introducing fluidizing gas into the reactor interior, wherein in the mounting position below the central tube a container is provided, into which opens a first conduit for supplying the process gas, and wherein in the mounting position below the tuyere bottom an annular space surrounding the central tube is provided, into which opens a conduit for supplying the fluidizing gas. Furthermore, this invention relates to a process for the chemical and/or physical treatment of fluidizable substances in such reactor.
From the prior art, fluidized-bed reactors as mentioned above are known, in which the annular space surrounding the central tube is attached to the central tube at a distance from the container. The walls of the central tube mostly are made of a high-temperature resistant stainless steel, in order to be able to withstand the high temperatures of frequently up to about 1000°C, which occur during the treatment of fluidizable substances. In addition, a cooling of the central tube frequently is provided, and for this purpose a narrow clearance mostly is created around the central tube, which partly is located inside the annular space for supplying the fluidizing gas, and through which for instance air of ambient temperature is passed.
Despite the cooling and the use of comparatively expensive high-temperature resistant stainless steel, not only the high temperatures inside the central tube can in part be controlled only with great difficulty, but in such reactors the entire construction is also regarded as worthy of improvement, in particular in terms of its rigidity and fatigue strength, especially in the case of a change in temperature (start-up and shutdown of the plant). Beside the thermal loads acting on the central tube, there are also mechanical loads as a result of the annular space for supplying the fluidizing gas, which supports on said central tube.
When using such reactors, the energetic efficiency also is regarded as worthy of improvement, as the cooling of the central tube, through which heated process gas is supplied, leads to a cooling of the process gas and hence to a deterioration of the efficiency.
Accordingly, it is the object of the present invention to create a reactor and a process as mentioned above, in which an improved energetic efficiency of the process can be achieved without impairment of the operational safety of the construction.
In accordance with the invention, this object substantially is solved in that in a reactor as mentioned above the metallic walls of the central tube, of the container and of the annular space are provided with a thermal insulating coating, wherein at least portions of the outer wall of the annular space form a continuous unit with the wall of the container. The lining of the metallic walls of the central tube, of the container and of the annular space provides for considerably reducing the thermal loads acting on these walls, in particular in the case of processes with higher temperatures of the process gas and/or fluidizing gas. At the same time, a substantially uniform temperature distribution is obtained in the walls of the container and of the annular space, so that no thermal stresses are generated in the transition region between these components. Due to the fact that the outer wall of the annular space forms a unit with the wall of the container, the mechanical loads acting on the central tube also are reduced considerably. Due to the inventive configuration of the fluidized-bed reactor, a constructively simpler and considerably stiffer construction thus is achieved, which better than known reactors can also withstand higher thermal and/or mechanical loads. In accordance with the present invention the term unit defines that the outer wall of the annular space adjoins the wall of the container and that said two walls are preferably fixed or attached to each other, e.g. by bonding or the like. However, this does not exclude that the two walls may be separated form each other, e.g. for replacement due to wear or the like.
In accordance with a preferred embodiment of the invention, the thermal insulating coating is formed by a lining with refractory concrete. The insulating coating can also include at least one layer of refractory brick and/or refractory concrete and/or a layer of light-weight refractory brick and/or insulating concrete. As a rule, a multilayer structure is used.
By means of the inventive construction of the fluidized-bed reactor, which effects a reduction of the thermal and mechanical loads as a result of thermal expansion, it is possible to manufacture the metallic walls of the central tube, of the container and/or of the annular space of a heat-resistant carbon steel. The same is much less expensive than the commonly used high-temperature resistant stainless steel, so that the manufacturing costs of the fluidized-bed reactor of the invention can be kept low.
When at least portions of the outer wall of the annular space support on the wall of the container, a particularly effective mechanical relief of the central tube can be achieved. The rigidity of the fluidized-bed reactor is further improved thereby. This also provides for a lateral introduction of the hot process gas with a high pressure of e.g. about 60 kPa into the container, without having to fear a damage of the reactor by stress peaks.
In accordance with a preferred embodiment of the invention, at least one compensator element is arranged in the central tube in the mounting position just below the tuyere bottom for compensating temperature-related changes in length of the central tube. It is recommendable, for instance, to provide the compensator element in the mounting position between the tuyere bottom and the second conduit for supplying the fluidizing gas. Hence, the compensator element is disposed inside the central tube so as to be easily accessible. A manhole in direct vicinity of the compensator element also can contribute thereto. By compensating temperature-related changes in length, the compensator element itself reduces the stresses caused thereby inside the central tube. This also contributes to a reduction of the loads acting on the reactor in accordance with the invention.
In operation, it cannot be excluded that dust and/or fluidizable substances get into the container and/or into the annular space through the central tube or through the tuyere bottom. This can lead to a considerable impairment of the gas flow. In accordance with the invention, at least one opening for discharging dust and/or fluidizable substances therefore is provided in the container and/or in the annular space, in particular in the lower region each in the mounting position. In this way, clogging of the central tube or of the tuyere bottom or of the container or annular space provided thereunder can effectively be avoided, without this involving an increased cleaning effort.
The object underlying the invention furthermore is solved by a process for the chemical and/or physical treatment of fluidizable substances in a reactor, for instance in a fluidized-bed reactor as mentioned above, wherein process gas with a temperature of more than 400°C, preferably more than 600°C, particularly preferably more than 800°C is introduced into the reactor interior via a central tube, and fluidizing gas with a temperature of preferably more than 100°C is introduced into the reactor interior via a tuyere bottom. In accordance with the invention, the fluidizing gas is supplied via an annular space arranged below the tuyere bottom in the mounting position and surrounding the central tube, into which opens a conduit for supplying the fluidizing gas, without the walls of the central tube being cooled in addition. In other words, the process of the invention is designed such that the fluidizing gas can already be introduced into the reactor interior with a comparatively high temperature. Together with the likewise comparatively high temperature of the process gas introduced into the reactor interior, the energetic efficiency of the process can distinctly be improved thereby. Preferably, preheated return gas is used here as fluidizing gas.
The energetic efficiency of the process of the invention also is further improved by omitting an additional cooling of the central tube, as the central tube and hence also the preheated process gas passed through the same is not cooled by the additional cooling.
In accordance with a preferred embodiment of the process of the invention, the process gas is introduced into the reactor interior with a temperature of more than 1000°C, in particular with a temperature of more than 1150°C. Furthermore, the pressure of the process gas can be above 30 kPa, preferably above 45 kPa, in particular about 60 kPa. Furthermore, the temperature of the fluidizing gas introduced into the reactor interior preferably is above 200°C, in particular above 300°C.
The temperature in the reactor can be even higher than the temperature of the introduced gases, e. g. by internal combustion. This can be achieved by introduction of fuel, e. g. with a lance, into the reactor or mixing of the introduced gases with gaseous fuels before entering the reactor. Furthermore after burning of the introduced gases and/or burning the dust contained in the gases in the fluidized- bed reactor is possible.
The process of the invention and the fluidized-bed reactor of the invention can be used in particular for the calcination of ilmenite, e. g. reducing, or similar fluidizable substances, but also for calcining aluminum hydroxide, for preheating other substances, e.g. iron-containing ores, or for the combustion of substances in the fluidized-bed reactor.
Another example of the process of the invention consists in that in a calcining reactor hot waste gases, which also are contaminated with solids, are introduced into the reactor via the central tube. Inside the reactor, a lower temperature is obtained, which depends on the reaction taking place in the reactor and on the solids mass flow into the reactor. Preferably, this type of reactor is utilized for processes in which a combustion of the fuel inside the reactor cannot be performed due to the low reactor temperature or can only be realized by expensive, low-burning fuels, such as butane. For the calcination of clay, for instance, a reactor temperature of 650°C is desirable, which is achieved by supplying a hot waste gas of up to 1200°C. Depending on the requirements of the end product, the hot gas can be generated by the combustion of fuels burning without residue, such as natural gas or the like, or by the combustion of ash-containing fuels, such as coal, biomass or the like, in combustion chamber before the reactor, possibly in conjunction with gas cleaning.
The invention will subsequently be explained in detail by means of an embodiment and with reference to the drawing. All features described and/or illustrated form the subject-matter of the invention per se or in any combination, independent of their inclusion in the claims or their back- reference.
The only Figure schematically shows a sectional view of a section of a fluidized-bed reactor in accordance with the invention in a particularly preferred embodiment. The lower region of the schematically indicated fluidized-bed reactor 1 in the mounting position as shown in the Figure shows a reactor interior 2, in which fluidizable substances, such as ilmenite, are subjected to a chemical and/or physical, for instance thermal treatment, in particular to a reducing calcination.
A central tube 3, which in the Figure protrudes upwards into the reactor interior 2, opens into the reactor interior 2. In the mounting position, and downwards in the drawing, a container 4 with an enlarged diameter as compared to the central tube 3 adjoins the central tube 3. A first conduit 5, through which hot process gas is introduced with a temperature of for instance about 1250°C, opens into this container 4, which process gas then flows through the container 4 and the central tube 3 into the reactor interior 2.
Both the central tube 3 and the container 4 substantially are made of a heat- resistant carbon steel, which on the inside is lined with a layer 6 of a refractory concrete. This inner insulation of the central tube 3 and of the container 4 effects that an additional cooling of the central tube 3, for instance by means of ambient air, can completely be omitted. In the particularly preferred embodiment of the Figure, the upper part of the central tube 3 is made of a high-temperature resistant stainless steel, preferably without such lining.
In another embodiment, this upper part can completely be omitted, so that the central tube ends directly at the level of the tuyere bottom. In this special embodiment it is preferred that the tuyere bottom is arranged at an angle and/or the nozzles are omitted, so that the bottom only is a plate possibly lined with refractory bricks.
Parts of the bottom of the reactor interior 2 surrounding the central tube 3 preferably constitute a tuyere bottom 7 with a plurality of nozzles opening into the reactor interior 2. Different to the Figure, the bottom can be configured at an angle and need not be equipped with nozzles. In the mounting position below the tuyere bottom 7, an annular space 9 is formed by a wall 8, which surrounds the central tube 3. The wall 8 of the annular space 9 supports on the upper wall of the container 4 as seen in the Figure. Hence the central tube 3 substantially is liberated from mechanical loads by the annular space 9, and the construction of the reactor 1 becomes stiffer on the whole. At the same time, an approximately constant distribution of heat is achieved substantially along the entire length of the central tube 3 by including the central tube 3 in the annular space 9, so that there are no local load peaks as a result of different thermal expansions.
The wall 8 can also be made of a heat-resistant carbon steel and be lined with an insulating layer 10 e.g. of a refractory concrete on the inner side facing the central tube 3.
The insulating layers 6 and 10 effect that despite the different temperatures of the gases supplied through the annular space 9 and the central tube 3 an at least approximately equal temperature is obtained inside the metallic walls of the central tube 3, of the container 4 and of the wall 8, whereby thermal stresses can be reduced considerably.
A second conduit 11, through which fluidizing gas is introduced into the annular space 9 and via the same through the tuyere bottom 7 into the reactor interior 2, preferably opens into the annular space 9. The fluidizable substances present in the reactor interior 2 are fluidized thereby. As fluidizing gas, there is preferably used gas preheated to for instance about 350°C, possibly return gas.
In principle, it is also possible to not completely supply the annular space 9 with fluidizing gas, but to only separate a part thereof and supply the same with gas. In a further embodiment it is possible to also partly keep the annular space open and/or introduce or pass through no gas at all.
As shown in the Figure, both at the lower end of the container 4 in the mounting position and at the lower end of the annular space 9 in the mounting position, openings 12 and 13, respectively, are formed in the wall 8. The size of the openings 12 and 13 is dimensioned such that dust entrained by the process or fluidizing gas and/or fluidizable substances falling through the tuyere bottom 7 or the central tube 3 into the annular space 9 or into the container 4 can be discharged from the annular space 9 or from the container 4, in order to thus prevent clogging or plugging of the supply passages for the process or fluidizing gas.
The size of the container 4 is preferably designed such that this container can completely receive the material falling back into the central tube in the case of an unexpected shutdown of the reactor, without the supply conduit 5 being clogged. Likewise, the annular space 9 preferably is configured such that the material falling back cannot clog the supply conduit 11 in the case of a sudden shutdown.
In the upper region of the central tube 3, a compensator element 14 is provided, which in the illustrated embodiment is arranged just below the tuyere bottom and is easily accessible e.g. via a manhole 15 through the annular space 9. The compensator element 14 is suitable for absorbing e.g. temperature-related changes in length of the central tube 3. Thus, it can further decrease the loads acting on the central tube 3. List of Reference Numerals:
1 fluidized-bed reactor
2 reactor interior
3 central tube
4 container
5 first conduit (process gas)
6 insulating coating
7 tuyere bottom
8 wall
9 annular space
10 insulating coating
11 second conduit (fluidizing gas)
12 opening in the container 4
13 opening in the wall 8
14 compensator element
15 manhole
We claim
1. A fluidized-bed reactor for the chemical and/or physical treatment of fluidizable substances in a reactor interior (2), comprising at least one central tube (3) for introducing process gas into the reactor interior (2) and a bottom,
wherein in the mounting position below the central tube (3) a container (4) is provided, into which opens a conduit (5) for supplying the process gas, wherein an annular space (9) surrounding the central tube ' (3) is provided
wherein the metallic walls of the central tube (3), of the container (4) and of the annular space (9) are provided with a thermal insulating coating (6, lo),
wherein at least portions of the outer wall (8) of the annular space (9) form a unit with the wall of the container (4), and
wherein the container (4) provided below the central tube (3) is enlarged in diameter with respect to the central tube (3).
2. The fluidized-bed reactor as claimed in claim 1, characterized in that the bottom is a tuyere bottom (7) for introducing fluidizing gas into the reactor interior (2).
3. The fluidized-bed reactor as claimed in claim 2, characterized in that in the mounting position below the tuyere bottom (7) the annular space (9) surrounding the central tube (3) is provided, into which opens a second conduit (11) for supplying the fluidizing gas.
4. The fluidized-bed reactor as claimed in any of the preceding claims, characterized in that the insulating coating (6, 10) is formed by at least one layer or lining made of a refractory concrete.
5. The fluidized-bed reactor as claimed in any of the preceding claims, characterized in that the metallic walls of the central tube (3), of the container (4) and/or of the annular space (9) are made of heat-resistant carbon steel.
6. The. fluidized-bed reactor as claimed in any of preceding claims, characterized in that at least portions of the outer wall (8) of the annular space (9) support on the wall of the container (4).
7. The fluidized-bed reactor as claimed in any of the preceding claims, characterized in that in the central tube (3) in the mounting position just below the tuyere bottom (7), preferably in the mounting position above the second conduit (11) for supplying the fluidizing gas, at least one compensator element (14) is arranged for compensating temperature-related changes in length of the central tube (3).
8. The fluidized-bed reactor as claimed in any of the preceding claims, characterized in that in the container (4) and/of in the annular space (9), in particular in the lower region each in the mounting position, at least one opening (12, 13) is provided for discharging dust and/or fluidizable substances.
9) A process for reducing calcination of ilmenite, using the fluidized-bed reactor (1) as claimed in any one of the claims 1 to 8.